This invention relates generally to semiconductor devices and more particularly to the structure of buried hetero structure semiconductor lasers and semiconductor devices utilizing fully the characteristics of the junction using an InGaAsP quaternary compound semiconductor. Further particularly the present invention relates to the semiconductor laser devices described above which use the semiconductor devices of the InGaAsP quarternary compound semiconductor, to transistors having an excellent current amplification ratio and an excellent current blocking ratio and to the semiconductor lasers of the type described above having a small threshold current value but having high reliability.
Among conventional buried hertero structure semiconductor lasers, there is a structure in which the thickness of a semiconductor layer on an active layer is first increased sufficiently (.gtorsim.3 .mu.m), reverse triangular shaped mesa stripe is then formed and thereafter current block layers are selectively grown only on both sides of the mesa while leaving the mask for the stripe such as a silicon dioxide film on the surface of the mesa stripe. In accordance with this structure, since mesa etching is deep, the position and width of the active layer has been difficult to control. Though this problem can be solved by reducing the thickness of the semiconductor layer on the active layer, an electrode formed on the mesa surface and the active layer will be too near to each other if the thickness is reduced while the structure described above is used as such. In this case, the electrode metal will be alloyed and hence the problem of reliability will develop.
On the other hand, there is also known a structure in which current blocking layers due to p-n junction are first formed on both sides of the mesa and the entire portion including the mesa is then buried. This structure is shown in FIG. 2. In this sturcture, the greater the thickness of the current blocking layer, the higher becomes the breakdown voltage so that a high temperature high output operation becomes possible. However, it has been difficult to secure a sufficient thickness (e.g. at least 1 .mu.m) for the current blocking layer in the proximity of the mesa because the mesa is a forward mesa whose surface is smaller than that of the width and the semiconductor layer on the active layer is below 0.5 .mu.m. This is because a selective growing method is employed for the selective growth, and hence the growth will o-cur at those portions at which the growth is not desired, if the thickness of the current blocking layer is increased.
Long wavelength semiconductor layers oscillating in a 1 .mu.m band are known as semiconductor devices using an InGaAs layer. In other words, this is an example of the application of the long wavelength semiconductor laser to the buried layer, and the buried layer has a function as the current blocking layer. Moreover, control of a lateral mode becomes easy by use of InGaAs. However, no examination has been made on the junction using the InGaAsP layer.